There are previously known projection displays employing various technologies to achieve large display screen dimensions, e.g., greater than about 40 diagonal inches. Such displays include imaging devices selected from among cathode-ray, liquid crystal, plasma, and field emission technologies employed in single and multiscreen arrangements. Problems with such displays include high cost, poor luminance and uniformity, limited screen size, brightness, contrast ratio, resolution, and useful life (reliability).
When an array of such displays is configured in a multiscreen arrangement, additional problems arise because of difficulties in achieving visually seamless display boundaries among the displays. In particular, arrayed projection displays require precise image edge matching and uniformly bright luminance across the entire projected image. Multiscreen displays exacerbate any image matching and nonuniformity problems because each display provides a subdivided portion of a total image, the multiple boundaries of which must appear as inconspicuous as possible. Unfortunately, when using projection displays in a multiscreen arrangement, it is especially difficult to achieve a visually seamless display because of luminance and color nonuniformities and geometric distortions that typically exist from screen to screen and from the center-to-edge of each screen. These problems effectively eliminate magnetically deflected cathode-ray tube displays from use in arrays.
Projection displays employing digitally addressed light valves have evolved to a point where many of the above-described problems can be solved. In particular, liquid crystal light valves have enabled implementing cost-effective, high resolution displays, albeit with some remaining luminance, uniformity, contrast ratio, and life problems. Solutions to some of these problems are described in U.S. Pat. No. 6,043,797 for COLOR AND LUMINANCE CONTROL SYSTEM FOR LIQUID CRYSTAL PROJECTION DISPLAYS and U.S. Pat. No. 6,273,570 for COMPACT LIGHT PATH AND PACKAGE FOR LIQUID CRYSTAL PROJECTION DISPLAYS, both of which are assigned to the assignee of this application and are incorporated herein by reference.
Referring to Table 1, the displayable resolution of such displays has evolved from VGA to SXGA resolutions and formats. Applicants' current projection displays offer SXGA resolution images having a greater than 1000:1 contrast ratio on a 170 cm (67 inch) diagonal screen. This performance level has opened the market for such displays in non-arrayed configurations for use in command and control, conference room, board room, and high-end home theater applications. There is, of course, a market-driven demand for ever-increasing display performance and an ever-decreasing cost.
TABLE 1RESOLUTIONS:H × V PIXELS/FORMATSQVGA320 × 240W-QVGA480 × 240VGA640 × 480W-VGA852 × 480SVGA800 × 600XGA1024 × 768 W-XGA1365 × 768 SXGA1280 × 1024SXGA+1400 × 1050UXGA1600 × 1200W-UXGA1920 × 1200QXGA2048 × 1536480I Interlaced NTSC 480 Line TV (640 × 480)480PProgressive NTSC 480 Line TV (640 × 480)720PProgressive ATSC 720 Line HDTV (1280 × 720)1080I  Interlaced ATSC 1080 Line HDTV (1920 × 1080)1080P Progressive ATSC 1080 Line HDTV (1920 × 1080)
Various models of liquid crystal light valves (hereafter “LCDs”) are available including transmissive, reflective, monochrome, color, and small- and large-panel configurations. Small panel LCDs are commonly used in portable and conference room multimedia projectors. Their current resolution is limited to SXGA format on a 4.57 cm (1.8 inch) diagonal monochrome polysilicon (transmissive or reflective) LCD used in costly 3-path color video projectors. To achieve a useable projected image brightness, very intense light impinges on the LCDs and is magnified 33× to 100× by a projection lens to achieve a useable image size. Unfortunately, maintaining SXGA image quality with the 33× to 100× magnification ratio requires using a relatively expensive 11-15 element wide-angle projection lens. Moreover, the high intensity light impinging on the polysilicon LCDs causes their failure by rapid discoloration after about 10,000 hours of use. Also such LCD projection displays have a contrast ratio of less than about 500:1.
Some of the above-described problems have been overcome in projection displays employing a single large panel, LCD. An example of such a display employing a 16.2 cm (6.4 inch) full-color projection panel is described in the above-cited '316 application. Unfortunately, such LCDs are very inefficient, passing only about 7 percent of the impinging light. However, adequate projected image brightness can be achieved with a sufficiently bright light source and, fortunately, the overall cost is reduced, the contrast ratio is greater than 1000:1, and the projection lens is simpler.